Contact lens and production method for contact lens

ABSTRACT

It is an object of the invention to ensure in a series of contact lenses composed of an assorted plurality of contact lenses having mutually different optical characteristics such as refractive power or the like that each contact lens is capable of exhibiting advantageously and consistently a good wear comfort and tear fluid exchange. In order to attain the object, the present invention arranges each contact lens  10   a,    10   b,    10   c  making up the series contact lens designed and having mutually different optical characteristics in the optical zone, such that not only is a shape of the lens back surface  14  of the optical zone  28  identified, but a shape of the peripheral zone  30  is identified at least the outer peripheral zone  44  that contributes to wear comfort and tear fluid exchange.

TECHNICAL FIELD

The present invention relates generally to contact lenses of soft typeor hard type. More particularly, the invention relates to contact lensesof novel structure appropriate to being provided as a series containingan assorted plurality of contact lenses having optical characteristicsof various kinds, and capable of ensuring excellent wear comfort inevery optical characteristics, and to a method of manufacturing suchcontact lenses.

BACKGROUND ART

One shape known in the art and widely employed to date for both softcontact lenses and hard contact lenses (hereinafter referred tocollectively as “contact lenses”) is that depicted in FIG. 6(a), whichhas a back surface optical zone 50 formed in the center portion of theback surface of the lens and a back surface peripheral zone 52 formedalong the outer circumference of this back surface optical zone 50,while having formed in the center portion of the front surface of thelens a front surface optical zone 54 and a front surface peripheral zone56 formed along the outer circumference of this front surface opticalzone 54, thereby forming an optical zone 58 in the center area of thelens and a peripheral zone 60 situated in the peripheral area of thelens.

When designing the shape of such a contact lens 62, the typicalprocedure includes: to first establish the diametric dimension: D_(OZ)of the back surface optical zone 50 and the diametric dimension: D_(PZ)of the front surface optical zone 54, as well as designing the shape ofthe back surface optical zone 50 and back surface peripheral zone 52having a base curve of generally spherical shape conforming the shape ofthe wearer's cornea; to then establish lens thickness: t1 in a frontsurface junction (i.e. the connecting zone of the front surface opticalzone and back surface optical zone) 64; and to then design the shape ofthe front surface optical zone so as to give the required diopter power,as well as establishing appropriate shape for the front surfaceperipheral zone on the basis of a function or arbitrary curve, so that afront surface junction 64 and an edge portion (peripheral edge of thelens) 66 join up smoothly.

Meanwhile, if the peripheral zone of a contact lens is too thin, itbecomes difficult for the lens to consistently hold its shape, andparticularly in the case of a soft contact lens may make it difficult todistinguish the front from the back, which can pose a risk of problemsin handling. Also, since contact lenses are generally not provided on apurely “order-made” basis to wearer but are rather provided from aseries prepared and provided as a combination lenses with optical zonesthat come in predetermined suitable number of diopter powers, with thelenses most suitable for the wearer being selected from the series.Thus, for each contact lens in the series having different front surfaceoptical zone shapes in order to provide different diopter strengths, itis necessary to design lenses in such a way as to ensure consistentshape retention.

Thus, the typical practice in the past for a contact lens 62 like thatillustrated in FIG. 6(a) having generally uniform thickness throughoutthe entire optical zone and low diopter power (for example, −1.0 diopterpower) was to appropriately design the shape of the front surfaceperipheral zone 56 and the thickness dimension: t1 at the location of afront surface junction 64 so as to enable the lens to consistently holdits shape through the rigidity of the peripheral zone 60, therebydesignating this as the base lens shape, and to then design for thisbase lens shape the front surface optical zones 54 that give differentdiopter powers. When using this design method, a predeterminedacceptable minimum thickness is established with reference to the lensmaterial and the like, and in the event that the lens center thicknessis to thin owing to the diopter power of the front surface optical zone54, the thickness of the front surface junction 64 and peripheral zone60 is redesigned to be thicker, so that thickness at the lens center isat least equal to predetermined minimum thickness.

Specifically, where the required diopter power is more positive thanthat of the base lens, or where more negative but the absolute value ofdiopter power is small, the front surface optical zone 54 can bedesigned making the front surface junction 64 thickness and peripheralzone 60 shape generally uniform. Whereas if the diopter strength is muchmore negative than that of the base lens (e.g. −15 diopters), byredesigning lens thickness in the front surface junction 64 andperipheral zone 60 (in particular, a back surface junction 66 thickness:t2) to be greater than the base lens as shown in FIG. 6(b), for example,lens center portion thickness: t0 is obtained to be sufficient to ensurethat there are no problems in terms of strength or durability. Accordingto such design methods, none of the contact lenses in a series will haveperipheral zone lens thickness smaller than that of the base lens shape,so that each of them can considerably hold lens shape on the basis ofthe rigidity of the peripheral zone.

In contact lenses of a series designed on the basis of the design methoddescribed above, depending on the diopter power established for theoptical zone 58, and in particularly where diopter power issignificantly negative, it becomes necessary to design and manufacturelenses that differ in shape according to the magnitude of diopter power,not just in the front surface optical zone 54, but over the entire frontsurface of the lens including the front surface peripheral zone 56. Aresultant problem was that design and manufacture of contact lensesmaking up a series was tedious.

Additionally, research conducted by the inventors has shown that wherecontact lenses of series based on prior art design methods are provided,when diopter power differs among contact lenses of a given series, thethickness dimension of the peripheral zone 60 and mass associatedtherewith differ appreciably, which in some cases can result indifferences in the movement of the contact lens over the cornea due tothe action of the eyelid occurring with blinking, or the position ofrest of the contact lens on the cornea due to the effect of gravity orthe like, resulting in some instances in adverse effects on wear comfortand vision.

With the foregoing in view, it is therefore an object of the presentinvention to address these problems by providing contact lenses in aseries composed of a combination of contact lenses of novel structure,whereby even in cases where diopter power or other opticalcharacteristics differ, consistently good wear comfort can be achieved,while at the same time ensuring adequate shape retaining action by theperipheral zone and strength at the lens center.

It is a further object of the invention to provide a contact lens ofnovel shape effective for creating contact lenses of a series.

It is yet a further object of the invention to provide a novel method ofmanufacturing contact lenses, whereby contact lenses of a series may bemanufactured efficiently.

Specifically, while various shapes for the back surface peripheral zonehave been studied to date in consideration of tear fluid exchange andstability, the shape retaining effect of the peripheral zone thicknessdimension in soft contact lenses has received only a cursory examinationand is not viewed as particularly important. Research conducted by theinventors, however, has shown that the shape of the peripheral zone hassignificant effects on contact lens wear comfort and vision, and inparticular that appreciable thickness of the peripheral zone includingthe front surface junction can result in appreciably impaired wearcomfort owing to pressure applied by the eyelid and the like, as well asappreciable movement of the lens over the cornea by the eyelid duringblinking, or a tendency of the lens rest position to shift verticallydownward on the cornea due to the greater effect of gravity, or in othersuch problems.

DISCLOSURE OF THE INVENTION

The present invention has been developed based upon these newdiscoveries, and there will be described modes of the invention createdfor the purpose of addressing the above problems. Elements employed ineach mode described herein may be employed in any possible combination.It is to be understood that the modes and technical features of theinvention are not limited to those disclosed herein, but may otherwisebe recognized based on the teachings of the present invention disclosedin the entire specification and drawings or that may be recognized basedon concept of the invention recognized by those skilled in the art inthe light of the present disclosure.

(First Mode of the Invention Relating to Series Contact Lenses)

The invention in a first mode thereof relating to a series of contactlenses provided as an assorted plurality of contact lenses, each lensbeing formed with an optical zone in a lens center area and a peripheralzone in a lens peripheral area, by forming a back surface optical zonein a center portion of a lens back surface as well as forming a backsurface peripheral zone to an outer peripheral side of a back surfaceoptical zone, while forming in a center portion of a lens front surfacea front surface optical zone as well as forming a front surfaceperipheral zone to an outer peripheral side of the front surface opticalzone, and having an identical diameter dimension but mutually differentoptical characteristics in the optical zone, the series of contactlenses being characterized in that in the assorted plurality of contactlenses, a shape of the lens back surface is identical for each lens, anda shape of an area extending a predetermined width in a diametricaldirection of a peripheral portion in the front surface peripheral zoneis identical for each lens, whereby while a shape of a portion extendinga predetermined width in the diametrical direction of at least aperipheral portion in the peripheral zone is identical for each lens, ashape of the front surface optical zone differs among the lenses so thatthe optical characteristics of the optical zone differs among thelenses.

In the series of contact lenses according to this mode, by adopting anovel element which had not been conceived of to date, namely, a commonshape for the peripheral zone, it is now possible to use identical shape(including identical thickness dimension) for most of the peripheralzone regardless of which contact lens in the series is employed; andthereby to effectively and consistently provide the wearer with goodwear comfort, stable position of the lens the cornea, and visionregardless of the optical characteristics of the optical zone selectedon a wearer-by-wearer basis, as well as realizing dramatic improvementsin contact lens performance and reliability. Additionally, when a givenwearer must change the diopter power of a contact lens as myopia orother abnormal refraction progresses, the discomfort associated withwear of a contact lens with a different diopter power may be reduced oravoided.

Specifically, with a contact lens of a shape in accordance withconventional design methods, in the case of a diopter having highnegative refractive power, there is a tendency for the peripheral zoneto be thicker and therefore press against the eyeball or against theeyelid, and for the increased weight to cause the rest position of thelens on the cornea to shift downward, for example. The series contactlens according to this mode, on the other hand, since the shape of theperipheral zone is generally the same regardless of the level ofrefractive power, the discomfort associated with pressure on the eyeballor eyelid or a change in the rest position on the cornea, occurring witha change in set refractive power, can be reduced or avoided, therebyproviding consistently good wear comfort and optical characteristics.

Further, in the series contact lenses having standardized peripheralzone shape according to this mode, contact lenses whose optical zoneshave different refractive power and other optical characteristics maynevertheless afford similar wear comfort and fitting pattern to the eyedue to the generally identical shape of the peripheral zone, therebymaking it possible to share a single or small number of trial lenses foruse in fitting lenses to individual wearers, even where the opticalcharacteristics required differ depending on the individual wearer. Thismakes it possible to obviate the need to prepare trial lenses for eachset of optical characteristics of the optical zone.

Additionally, in this mode, it is preferable to standardize acrossdifferent lenses making up a series the maximum thickness in theperipheral zone including the front surface junction, thereby providinga greater level of advantage in terms of consistent wear comfort andvision correction among the contact lenses that make up the series. Inthis mode also, it is preferable to standardize across the differentlenses making up a series to establish the front surface junction, whichis the boundary between the front surface optical zone and the frontsurface peripheral zone, diametrically inward from the back surfacejunction, which is the boundary between the back surface optical zoneand the back surface peripheral zone, as well as standardizing, acrossthe different lenses making up a series, at least the shape of theperipheral zone situated peripherally outside the back surface junction,thereby more effectively realizing the benefit of standardizing theperipheral zone in the manner described above.

(Second Mode of the Invention Relating to Series Contact Lenses)

The invention in a second mode thereof relating to a series of contactlenses according to the first mode, characterized in that differentdegrees of refractive power of the optical zone are established in theassorted plurality of contact lenses so that optical characteristics ofthe optical zone differ, and a diameter of the front surface opticalzone is varied depending on differences in refractive power of theoptical zones. According to this mode, it is possible, while usingsubstantially identical shape lens diameter dimension (DIA) andperipheral zone shape in each contact lens making up the series, toreadily vary the refractive power of the optical zone, i.e. diopterpower. Also, while contact lenses constituting a series according tothis mode mutually different diametrical width dimension of theperipheral zone, corresponding to the difference in diameter of opticalzones due to the differences in refractive power established for opticalzones, it is nevertheless possible, within an area of the peripheralzone formed on and existing in a contact lens, for the entirety thereofto be of shape identical to the peripheral zone of another contact lensbelonging to the same series, but with different refractive power. Inthis mode also, in preferred practice each contact lens making up aseries will have mutually different optical zone center portionthickness, depending on differences in diopter power established for theoptical zones, whereby it becomes easier to employ the same giventhickness of the front surface junction among contact lenses making up aseries.

(Third Mode of the Invention Relating to Series Contact Lenses)

The invention in a third mode thereof relating to a series of contactlenses according to the first or second mode characterized in that thediameter of the front surface optical zone is set to within a range φ5mm-φ12 mm in each of the assorted plurality of contact lenses. This modemakes it possible for a contact lens of typical size to moreadvantageously assure vision correction by the optical zone, stabilityof the lens on the cornea and tear fluid exchange by means of theperipheral zone, and the like. Where diameter of the optical zone issmaller than φ5 mm it becomes difficult to ensure the required opticalarea, posing the risk that it will be difficult to provide the wearerwith consistent vision correction. On the other hand if the diameter ofthe optical zone is greater than φ12 mm it becomes difficult to ensureadequate diametrical width direction of the peripheral zone formed atthe periphery of the optical zone, posing the risk of a decline in tearfluid exchange and stabilization of lens wear position by the peripheralzone.

(Fourth Mode of the Invention Relating to Series Contact Lenses)

The invention in a fourth mode thereof relating to a series of contactlenses according to any one of the first to third modes characterized inthat different degrees of refractive power of the optical zone areestablished in the assorted plurality of contact lenses so that opticalcharacteristics of the optical zone differ, and a center portionthickness of the front surface optical zone is varied depending ondifferences in refractive power of the optical zones. According to thismode, it is possible, while using substantially identical shape lensdiameter dimension (DIA) and peripheral zone shape in each contact lensmaking up the series, to readily vary the refractive power of theoptical zone, i.e. diopter power, and to do so with particularly goodeffectiveness in cases where the refractive power of the optical zone isrelatively small. Furthermore, in cases where the optical zone has highrefractive power, by combining this mode with the aforementioned secondmode for example, it becomes even easier to vary the refractive power ofthe optical zone, i.e. the diopter power, while employing the same givenlens diameter dimension (DIA) and peripheral zone shape among contactlenses making up a series.

(Fifth Mode of the Invention Relating to Series Contact Lenses)

The invention in a fifth mode thereof relating to a series of contactlens according to the fourth mode, characterized in that the centerportion thickness of the optical zone is set to within a range of 0.02mm-0.70 mm in each of the assorted plurality of contact lenses.According to this mode, in a contact lens of typical size, it ispossible to ensure an optical zone diameter of a size able to assuregood vision, as well as to assure peripheral zone width dimension andshape able to assure stability of the lens on the cornea and tear fluidexchange, while making it possible to establish an optical zone centerportion thickness great enough to give adequate strength and durability.Where the center portion thickness in the optical zone is less than 0.02mm, it becomes difficult to assure adequate strength and durability,whereas if the center portion thickness in the optical zone exceeds 0.70mm, the peripheral zone including the front surface junction may becomeexcessively thick.

(Sixth Mode of the Invention Relating to Series Contact Lenses)

The invention in a sixth mode thereof relating to a series of contactlens according to any one of the first to fourth modes, characterized inthat different degrees of refractive power of the optical zone areestablished in the assorted plurality of contact lenses so that opticalcharacteristics of the optical zone differ among these lenses, and thedifferent degrees of refractive power of the optical zone areestablished within a range of −25 diopters to +25 diopters, with adifference of at least 5 diopters. According to this mode, in anycontact lenses for which have been established mutually differentdiopter powers over a wide range of at least 5 diopters, preferably atleast 10 diopters, it is possible to consistently provide a standardizedlevel of good wear comfort over the contact lens series, so as toachieve excellent commercial value. This mode is advantageously realizedby combining the aforementioned second mode and fourth mode, whereby itbecomes possible to provide series contact lenses over a refractivepower setting range of at least 5 diopters, preferably at least 10diopters, having identical peripheral zone shape, and accordingly torealize excellent contact lens manufacture and manufacturing costs asdescribed above, while also affording consistently good wear comfort andvision.

(Seventh Mode of the Invention Relating to Series Contact Lenses)

The invention in a seventh mode thereof relating to a series of contactlenses according to any one of the first to sixth modes characterized inthat in each of the assorted plurality of contact lenses, the frontsurface peripheral zone is composed of a first front surface peripheralzone situated on an inner peripheral side and a second front surfaceperipheral zone situated on an outer peripheral side, with a firstperipheral zone being formed between the first front surface peripheralzone and the lens back surface, and with a second peripheral zone beingformed between the second front surface peripheral zone and the lensback surface, the second peripheral zone having a shape that decreasesin thickness gradually going towards the outer peripheral side, and thatamong the assorted plurality of contact lenses, each the secondperipheral zone is of identical shape, and the first front surfaceperipheral zone forming the first peripheral zone has a smooth surfaceconnecting to both the front surface optical zone and the second frontsurface peripheral zone in the diametrical direction at a continuousface having a common tangent.

According to this mode, by varying the diametrical length of the firstperipheral zone, it is possible for contact lenses making up a series toadvantageously deal with even differences in diameter of the opticalzones, while holding down increase in the thickness dimension of thefirst peripheral zone, as well as facilitating design and manufacture ofthe first peripheral zone, and accordingly of the contact lens per se.Additionally, since the front surface of the lens has smooth shapeoverall from the optical zone to the first and second front surfaceperipheral zones, it is possible to realize better wear comfort.Further, in this mode, thickness and curvature in the first peripheralzone can be made identical rather than differing among contact lensesmaking up a series, even where the optical zones differ in diameter.

(Eighth Mode of the Invention Relating to Series Contact Lenses)

The invention in an eighth mode thereof relating to a series of contactlenses according to the seventh mode characterized in that the firstfront surface peripheral zone is represented by a cubic curve in thediametrical direction. In this mode, it is possible to design the firstfront surface peripheral zone relatively easily with a high degree offreedom, as well as to machine the actual lens by means of cutting orthe like.

(Ninth Mode of the Invention Relating to Series Contact Lenses)

The invention in a ninth mode thereof relating to a series of contactlenses according to the first to seventh modes characterized in thatwherein in each of the assorted plurality of contact lenses, thediameter of the front surface optical zone is smaller than the diameterof the back surface optical zone, while the front surface peripheralzone is composed of a first front surface peripheral zone situated on aninner peripheral side and a second front surface peripheral zonesituated on an outer peripheral side, and has a shape with the firstfront surface peripheral zone being in a location generallycorresponding to the back surface optical zone, and with the backsurface optical zone offset.

According to this mode, in contact lenses making up a series,diametrical length of the first peripheral zone is varied (while keepingthickness and curvature the same) in order to prevent increase of thethickness dimension of the first peripheral zone while more readilydealing with instances where, for example, the optical zone diametervaries, as well as further facilitating design and manufacture of thefirst peripheral zone, and hence of the contact lens.

In this mode, offset refers to a relationship in which the back surfaceand front surface of the first peripheral zone are parallel, with thethickness dimension made constant by means of giving identical curvatureto the back surface and front surface. The amount of offset refers tothe difference in radius of curvature of the offset back surface andfront surface. Preferably, the amount of offset is set to 0.03 mm-0.50mm. If the amount of offset is less than 0.03 mm, the first peripheralzone may become too thin and, depending on the lens material, may makeit difficult to achieve adequate strength and durability, whereas if theamount of offset is greater than 0.50 mm, the first peripheral zone maybecome too thick, with the risk of deteriorated wear comfort in allcontact lenses that make up the series.

(Tenth Mode of the Invention Relating to Series Contact Lenses)

The invention in a tenth mode thereof relating to a series of contactlenses according to the ninth mode, characterized in that in each of theassorted plurality of contact lenses, a first peripheral zone ofgenerally constant thickness is formed by the first front surfaceperipheral zone and the back surface optical zone, and the second frontsurface peripheral zone is situated in a location generallycorresponding to the back surface peripheral zone, the second frontsurface peripheral zone and back surface peripheral zone forming asecond peripheral zone that decreases in thickness going towards theouter peripheral side, the peripheral zone being composed of the firstperipheral zone and the second peripheral zone, and that in among theassorted plurality of contact lenses, each the second peripheral zonehas identical shape and each the first peripheral zone has identicalthickness, while the diametrical width dimension of the first peripheralzones varies. In this mode, the shape of the second peripheral zone isidentical in contact lenses making up a series, so that the peripheralzone is more standardized, as a result of which design and manufactureof contact lenses is further facilitated, and it becomes possible tomore consistently achieve stability of the contact lens on the corneaand tear fluid exchange by means of the peripheral unit.

Further, in this mode it is preferable for the diametrical widthdimension of the first peripheral zone to be 3.0 mm or less in anycontact lens making up the series, whereby a large diametrical widthdimension of second peripheral zone can be assured, and tear fluidexchange and stabilization of the contact lens on the cornea by thesecond peripheral zone can be made more consistent over all of thecontact lenses making up the series. Additionally, the mode isadvantageously employed in combination with the aforementioned secondmode, whereby design and manufacture of the peripheral zone can besimplified while maintaining generally constant lens outside diameter(DIA), even in cases where diameter varies depending on refractive powerof the optical zone.

(Eleventh Mode of the Invention Relating to Series Contact Lenses)

The invention in an eleventh mode thereof relating to a series ofcontact lenses according to any one of the first to tenth modescharacterized in that a molding material for the assorted plurality ofcontact lenses in a soft material containing silicone. While it has beenreported that soft materials containing silicone are effective inregards to oxygen permeability and the like, research conducted by theinventors has shown that such highly oxygen permeable,silicone-containing soft materials typically have a high frictionalcoefficient against the eyelid and a strong tendency to stick to theconjunctiva of the eye, resulting in a tendency to tack, or stick to orpress against the cornea during blinking. By implementing the presentinvention in series contact lenses consisting of silicone-containingsoft materials, it is possible to hold down thickness of the peripheralzone to a small level regardless of the magnitude of refractive power ofthe optical zone, as well as to provide consistent effect of theperipheral zone in terms of tear fluid exchange and positionstabilization, thereby holding down tack and sticking so as toadvantageously realize good wear comfort. In this mode, both hydratedcontact lenses and non-hydrated contact lenses are similarly targeted assilicone-containing soft materials.

(Twelfth Mode of the Invention Relating to Series Contact Lenses)

The invention in a twelfth mode thereof relating to a series of contactlenses according to any one of the first to eleventh modes,characterized in that in the assorted plurality of contact lenses, theYoung's modulus: y of the molding material is 0.2 MPa≦y≦2.0 MPa; and thevalue of average thickness: Tm of said peripheral zone is 0.05mm≦Tm≦0.30 mm.

Specifically, research conducted by the inventors has shown for thefirst time that balance between the thickness dimension of theperipheral zone and the Young's modulus of the molding material is animportant parameter in terms of good fit (wear comfort etc.) when acontact lens is worn. This mode is based upon this new discovery, andaccording to this mode, it is possible to permit appropriate movementover the cornea, as well as realizing good wear comfort.

Where y<0.2 MPa or where Tm<0.05 mm, while oxygen permeability of thecontact lens can be readily assured, the contact lens will also tend tostick to the cornea, adversely affecting movement of the lens over thecornea and tending to depress tear fluid exchange. On the other hand,where y>2.0 MPa or where Tm>0.30 mm, pressure on the bulbar conjunctivaby the peripheral zone of the contact lens is high with a correspondingtendency for wear comfort to be appreciably deteriorated. In this mode,the dimensions and properties of the contact lens refer to conditionsduring wear. In this case of a hydrated contact lens material forexample, these would represent the swelled state.

(Thirteenth Mode of the Invention Relating to Series Contact Lenses)

The invention in a thirteenth mode thereof relating to a series ofcontact lenses according to any one of the first to tenth modescharacterized in that in the assorted plurality of contact lenses, theYoung's modulus: y of the molding material is 300 MPa≦y≦1500 MPa; andthe value of average thickness: Tm of said peripheral zone is 0.08mm≦Tm≦0.50 mm.

This mode, as with the twelfth mode, was perfected on the basis of thediscovery that thickness dimension of the peripheral zone and Young'smodulus of the molding material are important parameters relating tocontact lens wear comfort and the like, and affords good motion of thecontact lens over the cornea and good wear comfort, particularly in thecase of a hard contact lens.

(Fourteenth Mode of the Invention Relating to Series Contact Lenses)

The invention in a fourteenth mode thereof relating to a series ofcontact lenses according to any one of the first to thirteenth modes,characterized in that the back surface peripheral zone has a curvingsurface with a radius of curvature greater than that of the back surfaceoptical zone in the diametrical direction. In this mode, during wear ofthe contact lens, the back surface peripheral zone is advantageouslyheld in a state of floating up from the cornea, thereby moderatingpressure against the bulbar conjunctiva by the edge portion, as well aspromoting tear fluid exchange. In particular, a circular arc shape orelliptic arc shape in the diametrical direction may be used as thecurving surface of the back surface optical zone, thereby facilitatingits design.

(Mode of the Invention Relating to a Contact Lens)

The invention further relates to a contact lens being formed with anoptical zone in a lens center area and a peripheral zone in a lensperipheral area, by forming a back surface optical zone in a centerportion of a lens back surface as well as forming a back surfaceperipheral zone to an outer peripheral side of a back surface opticalzone, while forming in a center portion of a lens front surface a frontsurface optical zone as well as forming a front surface peripheral zoneto an outer peripheral side of the front surface optical zone, thecontact lens characterized in that the diameter of the front surfaceoptical zone is smaller than the diameter of the back surface opticalzone on the one hand, and the front surface peripheral zone is composedof a first front surface peripheral zone situated on an inner peripheralside and a second front surface peripheral zone situated on an outerperipheral side, while by having a shape wherein the first front surfaceperipheral zone is offset to the back surface optical zone, with a firstperipheral zone of generally constant thickness being formed by thefirst front surface peripheral zone and back surface peripheral zone,and by situating the second front surface peripheral zone at a locationgenerally corresponding to the back surface peripheral zone, the secondfront surface peripheral zone and back surface peripheral zone form asecond peripheral zone that decreases in thickness going towards theouter peripheral side, the peripheral zone being composed of the firstperipheral zone and the second peripheral zone.

With a contact lens of structure according to this mode, it is possibleto establish identical shape for the second peripheral zone, even whenmanufacturing several types of lenses with different optical zonediameter and lens outside diameter (DIA), thereby facilitating lensdesign and manufacture, as well as giving consistent levels of lensstabilization during wear and tear fluid exchange by a second peripheralzone of specific shape. Thus, reliability and consistency of productquality may be improved. According to the present invention, byproviding a first peripheral zone extending with a given thickness inthe diametrical direction, it becomes possible to establish a smallervalue for maximum thickness dimension of the peripheral zone, regardlessof the diopter power of the optical zone, and to thereby provide variouslevels of refractive power together with good wear comfort, even incontact lenses of soft type consisting of silicone-containing softmaterials. Additionally, series contact lenses according to theinvention as set forth hereinabove may be realized advantageously bymeans of contact lenses of structure according to the invention.

In a contact lens of structure according to the present invention, it ispreferable to establish the thickness dimension of the second peripheralzone such that going diametrically outward it decreases at a constantrate with respect to a diametrical distance from the back surfacejunction. By designing the generally constant rate of constriction inthickness of the second peripheral zone going diametrically outward, itis possible to more advantageously avoid catching thereof on the eyelid,further improving wear comfort. Additionally, in order to design thethickness dimension in the lens center axis in the second peripheralzone to decrease going diametrically outward while holding down themaximum thickness dimension thereof, at a location lying the diametricaldirection from the lens center axis, relative position of the secondfront surface junction (the boundary of the first peripheral zone andthe second peripheral zone) and the back surface junction is establishedappropriately in consideration of the diopter power and material of thecontact lens, and a second front surface junction is establishedpreferably at a location within 3.0 mm in the diametrical direction fromthe back surface junction, more preferably within 2.0 mm in thediametrical direction from the back surface junction. By so doing, it ispossible to readily design a shape for the back surface peripheral zoneand second front surface peripheral zone whereby there can be achieved afirst peripheral zone having constant thickness dimension, and a secondperipheral zone whose thickness dimension decreases at a generallyconstant rate going diametrically outward, whereby it becomes possible,for example, to give the back surface optical zone, back surfaceperipheral zone, fist front surface peripheral zone, or second frontsurface peripheral zone the shape of a spherical face (a circular arcface viewed in cross section) having a center of curvature situated onthe lens center axis,

In a contact lens of structure according to the present invention, inpreferred practice the back surface peripheral zone will have a curvingshape whose center of curvature is situated on the lens center axis, andwhose radius of curvature is greater than that of the back surfaceoptical zone, by means of which the back surface peripheral zone has ashape that, as compared to a line extended from the back surface, floatsin the direction away from the cornea, so that pressure on the bulbarconjunctiva by the edge portion (outside peripheral edge of the contactlens) may be moderated.

(Mode of the Invention Relating to a Method of Manufacturing SeriesContact Lenses)

The invention further relates to a method of manufacturing a contactlens constituting a series of contact lens according to the inventiondescribed hereinabove, and is characterized in that an entirety of thelens back surface including the back surface optical zone and the backsurface peripheral zone, and an area of predetermined diametrical widthof at least the outer peripheral portion of the front surface peripheralzone are shaped by molding.

Specifically, in contact lenses constituting series contact lensesaccording to the invention, even where optical characteristics differamong optical zones, the lens back surface in its entirety and at leastthe outer peripheral portion of the front surface peripheral zone ofeach lens have identical shape, whereby it is a simple matter to formthese surfaces by means of molding forming using molds. Thus, it becomespossible to readily and consistently form the shapes of back surface andfront surface peripheral zone of lenses. In the method of the presentinvention, while it is possible to form the front surface optical zoneby molding as well, preferably, the front surface optical zone will beformed by means of cutting performed after molding of the lens backsurface and front peripheral zone. In particular, when employing themethod of the invention in a contact lens according to the eighth modehereinabove relating to series contact lenses, it is possible in contactlenses making up the series to mold the entire front peripheral zoneusing a mold of identical shape, for example, in which case it willsuffice to carry out a cutting process for the front surface opticalzone only. In the cutting process itself, it is simpler to control thecutting tool than is the case where the peripheral zone is shaped bycutting as well, making the process easier and faster.

(Mode of the Invention Relating to a Method of Manufacturing a ContactLens)

The invention further relates to a method of manufacturing a contactlens, characterized in that when manufacturing a contact lens beingformed with an optical zone in a lens center area and a peripheral zonein a lens peripheral area, by forming a back surface optical zone in acenter portion of a lens back surface as well as forming a back surfaceperipheral zone to an outer peripheral side of a back surface opticalzone, while forming in a center portion of a lens front surface a frontsurface optical zone as well as forming a front surface peripheral zoneto an outer peripheral side of the front surface optical zone, anentirety of the lens back surface including the back surface opticalzone and the back surface peripheral zone, and an area extending overpredetermined diametrical width of at least the outer peripheral portionof the front surface peripheral zone are shaped by molding, and thefront surface optical zone of the lens front surface is then shaped bycutting.

According to the method of the present invention, by changing thecutting pattern of the front surface optical zone in order to modifyappropriately the shape of the front surface optical zone, it is asimple matter to establish various optical characteristics.Additionally, since areas other than the front surface optical zone,namely, the back surface optical zone, the back surface peripheral zone,and the front surface peripheral zone, are all formed by means ofmolding, these are easy to manufacture. In particular, since opticalcharacteristics are determined by the shape of the front surface opticalzone, it is possible to standardize mold shape for contact lenses ofwhich different optical characteristics are required, so thatmanufacturing cost may be improved. Additionally, as compared to thecase where both the front surface optical zone and the front surfaceperipheral zone are formed by cutting, the fact that only the frontsurface optical zone is formed by cutting makes it easier to control thecutting tool, making possible further improvement in manufacturing costand reduction in time required for manufacture.

In the method of manufacturing a contact lens pertaining to the methodof the invention, it is preferable to set minimum lens thickness in saidoptical zone of said lens front surface prior to shaping by cutting towithin the range 0.05 mm-1.0 mm. If minimum lens thickness is less than0.05 mm, depending on the lens material, adequate component strength maynot be displayed during the cutting process of the optical zone, with arisk of a deformation-induced drop in machining accuracy, breakage orother problem. Whereas, if minimum lens thickness is greater than 1.0mm, the cutting process will require an extended period of time, and aconsiderable amount of material will need to be cut, posing the risk ofa significant load on the cutting tool or other problems.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows radial sectional views (a), (b), (c) of three exemplarycontact lenses making up a series of contact lenses in a firstembodiment of the invention.

FIG. 2 is an enlarged fragmentary view of the contact lens shown in FIG.1(a).

FIG. 3 is a radial sectional view showing a specific example of a moldforming mold for use in forming the contact lens shown in FIG. 1.

FIG. 4 shows radial sectional views (a), (b), (c) of three exemplarycontact lenses making up a series of contact lenses in a secondembodiment of the invention.

FIG. 5 is an enlarged fragmentary view of the contact lens shown in FIG.4(a).

FIG. 6 shows radial sectional views (a), (b) of two exemplary contactlenses making up a conventional series of contact lenses.

BEST MODE FOR CARRYING OUT THE INVENTION

In order to illustrate the invention more concretely, the embodiments ofthe invention are described in detail hereinbelow, making reference tothe accompanying drawings.

FIGS. 1(a), (b), and (c) depict as one embodiment of the invention aplurality of contact lenses 10 a, 10 b, 10 c selected appropriately froma series of contact lenses. The series contact lenses are composed ofcombinations of a plurality of contact lenses whose optical zones havemutually different optical characteristics, for example, differentrefractive power (diopter power), and are provided to the wearer throughsuitable selection, from among the plurality of contact lenses, of onecontact lens having optical characteristics appropriate for the wearer.The selection is made on the basis of the results of an examination ofthe optical system of the eye of the wearer by an ophthalmologist orother examiner. Here, the contact lenses 10 a, 10 b, 10 c which areconstituent elements of a series of contact lenses each have a shapethat overall has the form of a partial spherical shell, and is intendedto the worn in the usual manner, i.e. superimposed on the surface of thecornea of the eye. Each of the contact lenses 10 a, 10 b, 10 c of thisembodiment has a lens center axis 12 constituting the optical axis, i.e.the optical center axis of the optical zone, and since each contact lens10 a, 10 b, 10 c is formed as a body of rotation shape about this lensoptical axis 12, only radial cross section is shown in each of FIGS.1(a), (b), and (c). To facilitate understanding, an enlargedillustration of contact lens 10 a is shown in FIG. 2. The followingdescription makes reference to both FIGS. 1 and 2. In the followingdescription, as a general rule the “radial direction” of contact lenses10 a, 10 b, 10 c refers to the direction of a straight line at a rightangle to the lens optical axis 12; “radial dimension” and “radial widthdimension” refer to dimensions extending on the line in the direction ofthe straight line.

To describe in more detail, each contact lens 10 (herein, in the casethat specific symbols a, b, c are absent, lenses a, b, and c arereferred to collectively) has a lens back surface 14 of generallyspherical concave surface shape. This surface is formed by a backsurface optical zone 16 located in the central portion and a backsurface peripheral zone 18 located in the peripheral portion. The lensfront surface 20 is of generally spherical convex surface shape, thisface being formed by a front surface optical zone 22 located in thecentral portion and a front surface peripheral zone 24 located in theperipheral portion. The back surface optical zone 16 and front surfaceoptical zone 22 are each circular in front view along the direction ofthe optical axis 12, while the back surface peripheral zone 18 and frontsurface peripheral zone 24 are each of annular shape in front view. Anannular edge portion 26 is formed around the entire circumference of thecontact lens 10. By means of this edge portion 26, the back surfaceperipheral zone 18 and front surface peripheral zone 24 are connectedtogether at their outer peripheral edges.

Also formed in the contact lens 10 in the center portion thereof is anoptical zone 28 having a suitable level of refractive power for visioncorrection, the zone having circular shape in front view. This opticalzone 28 is formed in an area bordered on either side by the back surfaceoptical zone 16 and the front surface optical zone 22. To the outerperipheral side of optical zone 28 is formed a peripheral zone 30 ofannular shape of predetermined width in front view, extending betweenthe optical zone 28 and the edge portion 26. This peripheral zone 30 isformed in an area bordered on either side by the outside peripheralportion of the back surface optical zone 16 or the back surfaceperipheral zone 18 and the front surface peripheral zone 24, and has anaction of promoting tear fluid exchange during wear, and of stablyretaining the contact lens 10 in the appropriate position on the cornea.

Dimension and shape of the optical zone 28 and peripheral zone 30, andtheir constituent back surface optical zone 16, back surface peripheralzone 18, front surface optical zone 22, and front surface peripheralzone 24 are determined appropriately in consideration of the shape anddimensions of regions such as the wearer's cornea, pupil, and eyelid,and of the optical characteristics required, and as such are notlimited. However, to facilitate understanding herein, the descriptionemploys specific numerical values by way of example.

Specifically, in this embodiment, the diameter dimension (outermostdiameter dimension, designated as DIA) of contact lenses 10 is ofconstant size established within the range 13-15 mm. The diameter Drj ofthe back surface junction 32 which is the boundary of the back surfaceoptical zone 16 and the back surface peripheral zone 18 is equal toabout 80% of the DIA. The diameter dimension Dfj of the first frontsurface junction 34 which is the boundary of the front surface opticalzone 22 and the front surface peripheral zone 24 is smaller than that ofthe back surface junction 32. The diameter dimension of the first frontsurface junction 34, specifically, the diameter of the front surfaceoptical zone 22, is established within the range φ5 mm-φ12 mm.

Here, the back surface optical zone 16 is given a spherical concavesurface generally corresponding to the shape of the surface of thecornea of the wearer in order to provide good wear comfort. It is given,for example, a spherical surface with a radius of curvature Rr havingthe curvature center on the lens center axis 12. In order to achievegood tear fluid exchange, the back surface peripheral zone 18 is given,for example, a spherical surface with a radius of curvature Rrp largerthan that of the back surface optical zone 16, and having the curvaturecenter on the lens center axis 12. By so doing, the back surfaceperipheral zone 18, with the back surface junction 32 as a point ofsupport, is disposed floating up slightly from the corneal surface asone moves diametrically outward, thereby reducing pressure on the bulbarconjunctiva by means of a “hinge” action so as to improve wear comfort,as well as improving tear fluid exchange. The back surface junction 32will preferably be formed with an appropriately chamfered, rounded edgehaving a small radius of curvature, so as to avoid an intersect pointconfiguration having corners in the diametrical cross section of thelens.

In order to produce in the optical zone 28 the optical characteristicsrequired to correct the vision of the wearer, the front optical zone 22is designed in consideration of the shape of the back surface opticalzone 16. For instance, where correcting for myopia or correcting forhypermetropia, and where the back surface optical zone 16 is a sphericalsurface, it will be designed by selecting a spherical surface shapehaving a radius of curvature Rf that differs from the radius ofcurvature Rr of the back surface optical zone 16 and having its centerof curvature on the lens center axis 12, so as to give the appropriatediopter power (negative or positive diopter).

The front surface peripheral zone 24 extends between the outerperipheral edge of the front surface optical zone 22 and the edgeportion 26, with the inner peripheral edge of the front surfaceperipheral zone 24 connecting to the outside peripheral edge of thefront surface optical zone 22 at the first front surface junction 34. Inthe diametrically medial portion of the front surface peripheral zone 24is formed a second front surface junction 36 which is a curvatureinflection point. With this arrangement, the front peripheral zone 24 iscomposed of a first front surface peripheral zone 38 of annular shape infront view, situated between the first front surface junction 34 and thesecond front surface junction 36, and a second front surface peripheralzone 40 of annular shape in front view, situated between the secondfront surface junction 36 and the edge portion 26.

The relative spacing dimension of the second front surface junction andback surface junction 32 in the diametrical direction is preferably 3.0mm or less, more preferably 2.0 mm or less. In the illustratedembodiment in particular, diametrical dimensions of the first frontsurface junction 34 and the back surface junction 32 are generally thesame (Drj). The diametrical distance between the first front surfacejunction 34 and the second front surface junction 36, in other words,the diametrical width direction of the first front surface peripheralzone 38, is preferably set to 3.0 mm or less. In this embodiment, by sodoing, the peripheral zone 30 is divided shapewise into two, i.e. aninner peripheral side and an outer peripheral side, thereby forming afirst peripheral zone 42 in an area bordered on either side by the firstfront surface peripheral zone 38 and the back surface peripheral zone16, as well as forming a second peripheral zone 44 in an area borderedon either side by the second front surface peripheral zone 40 and theback surface peripheral zone 18. That is, in this embodiment, thediametrical width dimension of the first peripheral zone 42 havingconstant thickness dimension is the same as the diametrical widthdimension of the first front surface peripheral zone 38 [(Drj−Dfj)/2],and the width dimension thereof is 3.0 mm or less.

The first front surface peripheral zone 38 has a bowed surfaceoffsetting the back surface optical zone 16, and has the same centerpoint: O as the back surface optical zone 16, as well as being formedwith a radius of curvature: Rfp=Rr+α that is greater by a predeterminedamount of offset: a than the a radius of curvature: Rr of the backsurface optical zone 16. With this arrangement, the first back surfaceperipheral zone 38 is given generally constant thickness dimension (α)over its entirety. The amount of offset: a is preferably set within arange of 0.03 mm-0.5 mm in consideration of the lens material and thelike; in this embodiment, α=0.2 mm.

Additionally, the second front surface peripheral zone 40 is situatedextending outwardly beyond the back surface peripheral zone 24. Theshape of the second front surface peripheral zone 40 does not offset theback surface peripheral zone 24, but is designed especially inconsideration of the shape of the back surface peripheral zone 24, withthe thickness dimension of the portion bordered on either side by thesecond front surface peripheral zone 40 and the back surface peripheralzone 24 gradually decreasing as one moves diametrically outward from theback surface junction 32 towards the edge portion 26. In particular, inthis embodiment, the thickness dimension in the direction parallel tothe lens center axis 12 in the second peripheral zone 44 is establishedaccording to the equation below, so as to decrease at a constant rate(Rate) in the diametrical direction as shown in FIG. 2.Rate=(T 1−T 2)/(X 2−X 1).

T1 denotes the thickness dimension of the inner peripheral edge of thesecond peripheral zone 44, and T2 denotes the thickness dimension of theouter peripheral edge of the second peripheral zone 44. X1 is thediametrical distance of the inner peripheral edge of the secondperipheral zone 44 from the lens center axis 12, and X2 is thediametrical distance of the outer peripheral edge of the secondperipheral zone 44 from the lens center axis 12.

In FIG. 2 are shown by way of example specific numerical values forthickness dimension in a second peripheral zone 44 designed according tothis embodiment, having a lens thickness dimension T1=0.25 mm in theinner peripheral edge portion of the second peripheral zone 44, as wellas a lens thickness dimension T2=0.14 mm in the outer peripheral edgeportion of the second peripheral zone 44.

In order to avoid an intersect point configuration having corners in thediametrical cross section of the lens, the first front surface junction34 and the second front surface junction 36, like the back surfacejunction 32, preferably join at surfaces bordering the junction 34, 36to either side in the diametrical direction connected by a commontangent, or at surfaces to either side connected by an appropriatelychamfered, rounded surface having a small radius of curvature.

Here, the second front surface junction 36, together with the outsidediameter dimension (DIA) of the edge portion 26, is fixed in eachcontact lens 10 making up the series of contact lenses. With thisarrangement, the second peripheral zone 44 in each of the contact lenses10 a, 10 b, 10 c can be formed in its entirety with the same shapehaving the same thickness dimension and radius of curvature at the samelocation in the lens outer peripheral portion.

Likewise, in each of the contact lenses 10 a, 10 b, 10 c, the firstperipheral zone 42 can be formed with the same thickness dimensionthroughout its entirety, and mutually identical values for thicknessdimension: T1 (or α) thereof can be established for it.

The diametrical location of the first front surface junction 34, inother words the diametrical location of the inner peripheral edge of thefirst peripheral zone 42, that is, the diametrical width dimension ofthe second peripheral zone 42 differs as needed among the contact lenses10 a, 10 b, 10 c that make up the contact lens series. At least thecontact lens having the optical zone 28 whose diopter value: P ishighest on the negative side will have its first front surface junction34 situated further inward in the diametrical direction than will thecontact lens having the optical zone 28 with the diopter value closestto 0.

Here, diametrical location of the first front surface junction 34 isdetermined such that, where the shape of the front surface optical zone22 is designed with the thickness dimension of the outer peripheralportion of the front surface optical zone 22 is the thickness dimensionof the first front surface junction 34 (in this embodiment, α=0.2 mm),lens thickness: Tc at the lens center axis 12 is not smaller than theminimum allowable thickness established in consideration of the lensmaterial and other factors. That is, where the minimum allowablethickness is 0.07 mm, the diametrical location of the first frontsurface junction 34 is manipulated such that Tc≧0.07 mm. In preferredpractice, the diametrical dimension: Dfj of the first front surfacejunction 34 from the center axis 12 is such that 2.5 mm≦Dfj≦6.0 mm. Ifthe value of this diametrical dimension: Dfj is smaller than 2.5 mm, theoptical zone will become too small, with the risk of making it difficultto consistently achieve effective vision correction; if on the otherhand the value of this diametrical dimension: Dfj is greater than 6.0mm, there is a risk of making it difficult to ensure adequatediametrical width dimension on the part of the second peripheral zone44, possibly resulting in impaired tear fluid exchange action and lensposition stabilizing action by the second peripheral zone 44.

Under design conditions for the peripheral zone 30 in an embodiment likethat shown in FIG. 2, where the diopter power of the optical zone 28 hasbeen set to −1.00 diopter, −7.00 diopters, and −15.00 diopters,respectively, the specific designed shapes of the front surface opticalzone 22 will be as shown in FIGS. 1(a), (b) and (c). As shown in FIG. 1,in the series of contact lenses of this embodiment, the diametricaldimension of the front surface optical zone 22 is established throughadjustment with reference to the diopter power established for theoptical zone 28. As noted, in each of the contact lenses 10 shown inFIGS. 1(a), (b) and (c), the second peripheral zone 44 has identicalshape, while the first peripheral zone 42 is a spherical shape spreadingout with the same thickness dimension and same curvature.

Accordingly, in series of contact lenses having the structure describedabove, each of the contact lenses 10 a, 10 b, 10 c making up the serieshas mutually identical shape at a minimum in the second peripheral zone44 which is a zone of predetermined diametrical width in the outerperipheral portion of the peripheral zone 30, whereby the tear fluidexchange action and lens position stabilizing action afforded by thesecond peripheral zone 44 can be effectively and consistently displayedregardless of which contact lens 10 a, 10 b, 10 c is selected.

Furthermore, in each of the contact lenses 10 a, 10 b, 10 c, not only isthe shape of the second peripheral zone 44 the same, but the thicknessdimension of the first peripheral zone 42 formed to the inner peripheralside thereof is the same over the entire extension thereof, wherebyregardless of the diopter power of the optical zone 28, the lens maximumthickness dimension will be identically thin, and thus even in a contactlens having high negative diopter power, a thicker peripheral zone 30can be avoided, the impaired wear comfort associated with a thickerperipheral zone 30 can be prevented, and good wear comfort can beadvantageously and consistently achieved.

In this embodiment, not only the diametrical dimension of the frontsurface optical zone 22, but also the lens center thickness: Tc isadjusted depending on the diopter power established for the optical zone28, whereby lens thickness in the peripheral zone can be madeconsistently thin, while adequate diametrical dimension: Dfj on the partof the optical zone 28 can be advantageously assured, even where acontact lens has high negative diopter power, so that the opticalcharacteristics required of the optical zone 28 can be effectivelyachieved.

In the peripheral zone 30, as noted, on the basis of the diametricalwidth dimension needed in order to advantageously produce tear fluidexchange action and the like on the part of a second peripheral zone 44able to provide tear fluid exchange action and the like, there is formedan area of predetermined diametrical width in the outer peripheralportion, as well as forming a first peripheral zone 42 that extends withgenerally constant thickness dimension towards the inner peripheralside. Therefore, even in a contact lens 10 a having diopter power(diopter value) of close to 0, it is possible to advantageously form theperipheral zone 30 with adequate diametrical width dimension whilekeeping its maximum thickness at a minimum, and as a result to reducethe thickness and mass of the peripheral zone 30, ensuring furtherimprovement in wear comfort and proper stable positioning of the lens.

The results of clinical tests conducted using the contact lens 10 ashown in FIG. 1(a), whose optical zone 28 has diopter power (P) of−1.00, and the contact lens 10 b shown in (b), whose optical zone 28 hasdiopter power (P) of −7.00, are shown in Table 1 appearing below. Eachcontact lens 10(a), 10(b) was of soft type consisting ofsilicone-containing non-hydrated soft material (Young's modulus (y)=0.5MPa), DIA=14.0 mm, Drj=11.0 mm, Rr=8.4 mm, and α=2.0 mm; othermorphological details are in accordance with FIGS. 1 and 2.

Clinical tests similar to those in this example were also carried outusing contact lenses of conventional structure, namely, as shown inFIGS. 6(a) and (b), contact lenses 62 a, 62 b of shape determined byconventional design methods, having a back surface optical zone 50 andback surface peripheral zone 18 identical in shape to those in theexample, and optical zone 58 diopter power (P) of −1.00 and −7.00, thesame as in the example. Data for these Comparative examples is given inthe Table 1 as well. In each of the contact lenses 62 a, 62 b of theComparative examples, the front surface peripheral zone 56 was ofspherical shape having a single radius of curvature over the entiretythereof, in accordance with conventional structure. The contact lenses62 a, 62 b of Comparative examples are soft contact lenses of samesilicone-containing soft material as those in the example. TABLE 1Examples Comparative Examples P = −1.00 P = −7.00 P = −1.00 P = −7.00Evaluation item (diopters) (diopters) (diopters) (diopters) fittingNormal Normal Normal Loose amount of lens motion 1.0 mm 1.0 mm 1.0 mm2.0 mm lens rest position center center center lower side pressure bylens no no pressure pressure peripheral zone pressure pressure wearcomfort good good poor poor stability of vision stable stable stableunstable

From the clinical results given in Table 1, it will be apparent that thecontact lenses of the example afford consistently good wear comfort andlens stability, irrespective of the magnitude of the diopter powerestablished for the optical zone 28.

For contact lenses consisting of soft materials (silicone-containingtypes) having Young's modulus (y) values of 0.2-2.0 MPa, and contactlenses consisting of hard materials (oxygen permeable types) havingYoung's modulus (y) values of 300-1500 MPa, tests were conducted in thesame manner as the clinical tests described above, while varying thethickness dimension of the peripheral zone 30 of each. As a result, itwas found that in both soft and hard contact lenses, if the thicknessdimension of the peripheral zone 30 is too small, particularly for alens consisting of oxygen permeable material, while oxygen permeabilitywill be generally good, the contact lens will tend to stick to thecornea or bulbar conjunctiva, so that movement of the contact lens overthe eye is poor and tear fluid exchange tends to decline. With softlenses, whereas, there is an additional risk of poor handling due toinability to distinguish between back and front, or other problems. Onthe other hand, if the thickness dimension of the peripheral zone 30 istoo great, there will be considerable pressure against the bulbarconjunctiva by the peripheral zone of the contact lens, as well as atendency for wear comfort to be adversely affected, and other problems.

Accordingly, it is necessary to design the thickness of the peripheralzone 30 appropriately in consideration of the required contact lenscharacteristics, and in this regard it became clear that appropriatethickness dimension of the peripheral zone 30 differs appreciablydepending on the Young's modulus (y) of the contact lens material.

Testing and verification conducted by the inventors has clearly shownthat in the case of a soft contact lens of a contact lens moldingmaterial with a Young's modulus: y value of 0.2 MPa≦y≦2.0 MPa,peripheral zone 30 average thickness: Tm values such that 0.05mm≦Tm≦0.30 mm are effective. On the other hand, in the case of a hardcontact lens of a contact lens molding material with a Young's modulus:y value of 300 MPa≦y≦1500 MPa, peripheral zone 30 average thickness: Tmvalues such that 0.08 mm≦Tm≦0.50 mm are effective, in terms of achievingbetter wear comfort.

In preferred practice, the Young's modulus of a contact lens materialwill be measured using a test piece of shape appropriate for the targetcontact lens. Where a thick, large test piece is employed withoutconsideration of contact lens product shape, since even for a givenmaterial, the processing time for each step and other aspects of themanufacturing process different between a test piece taken from a largeblock and a thin molded contact lenses, the physical properties of thesewill differ to an extent that cannot be ignored. Specifically, it ispossible to use a commercially available universal materials tester asthe testing machine, for example, Model 4301 from Instron Japan Inc. Asthe test piece, it is preferable to use as the test piece a special onehaving a generally dumbbell shape in plan view and total length ofapproximately 12-25 mm, produced by punching out a molded sheet profileof thickness of approximately 0.75 mm±0.05 mm, and integrally molding atboth ends thereof wide grip portions to a center portion that extendslinearly with a constant cross section of predetermined width dimension.

Following is a description of a specific example of an advantageousmethod of making contact lenses 10 of this embodiment having thestructure set forth hereinabove.

When making the contact lens 10, first, as shown in FIG. 3, there isprepared a forming mold 102 with a mold cavity 100 corresponding inshape of the shape of the target contact lens 10. This forming mold 102is of split structure comprising a lower mold 104 and an upper mold 106.By mating the two molds together, the mold cavity 100 is produced at themating faces of the lower and upper molds 104, 106.

Here, a mold face 108 serving as the cavity-forming face of the uppermold 106 is shaped with shape substantially identical to the entire lensback surface of the target contact lens 10, including the back surfaceoptical zone 16 and back surface peripheral zone 18. On the other hand,a mold face 110 serving as the cavity-forming face of the lower mold 104is shaped in the outer peripheral portion 112 thereof with shapesubstantially identical to the front surface peripheral zone 24 of thetarget contact lens 10, and in the center portion 114 thereof generallyoffsets the front surface optical zone 22 outwardly from the curvaturecenter thereof so as to form a center portion thicker than the opticalzone 28 of the target contact lens 10.

The optical zone 28 of the target contact lens 10, which must be takeninto consideration when establishing the shape of the center portion 114of the mold face 110, is the thickest optical zone 28 among all of thecontact lenses 10 of various diopter powers making up the contact lensseries. With this arrangement, the forming mold 102 can be used duringmolding of all of the contact lenses 10 of various diopter powers makingup the contact lens series.

That is, when using such a forming mold 102 to form contact lenses 10,the mold face 110 of the opened lower mold 104 is opened facing upward,and a predetermined amount of monomer material for molding the contactlens is injected therein. The upper mold 106 is then juxtaposed againstthe lower mold 104 from above so that the monomer material fills themold cavity 100 defined between the lower and upper molds 104, 106.Then, the monomer material is subjected to some suitable process such asirradiation with ultraviolet, heating, or the like, to promotepolymerization, thereby molding a contact lens blank.

The contact lens blank obtained in this manner has a lens back surfacethe entirety of which is the same shape desired of the target contactlens 10. The lens front surface, in the first and second front surfaceperipheral zones 38, 40 thereof, is also of the same shape desired ofthe target contact lens 10. That is, the contact lens blank is moldedinto generally the same shape as the target contact lens 10, with theexception of substantially all of the front surface optical zone 22.

The contact lens blank is then subjected to a cutting process of thefront surface optical zone 22 thereof only, to complete the targetcontact lens 10. The cutting process may be carried out advantageouslyon the contact lens blank while it is still deposited on the lower mold104, by gripping the lower mold 104 in the chuck of the cuttingapparatus and cutting the contact lens blank with the appropriate biteas it revolves about the lens center axis, for example.

According to this manufacturing method, it is possible to mold theentire contact lens, except for the front surface optical zone 22, bymeans of a forming mold 102 with substantially a single shape, and tothen simply by adjusting the amount of cutting of the front surfaceoptical zone 22, produce contact lenses 10 a, 10 b, 10 c with differentdiopter powers in the series of contact lenses, thereby making itpossible to manufacture series contact lenses very efficiently.

Additionally, when making contact lenses 10 that have different opticalcharacteristics such as diopter power, since peripheral zones 30 aremolded with identical shape, the level of polymerization shrinkage ofthe monomer material, which differs with shape such as thicknessdimension, will be generally the same for each contact lens 10 a, 10 b,10 c making up a contact lens series, which provides the significanttechnical advantage that a high degree of shaping accuracy can beconsistently assured.

Also, when cutting a contact lens blank, since the front surfaceperipheral zone 24 is molded into the target shape, it is sufficientsimply to subject the lens front surface 20 to a cutting process, makingit easy to control the cutting tool and other factors, so that simplercontrols and cutting apparatus may be used, and the cutting process maybe accomplished quickly.

The extent of cutting (cutting depth) of the front surface optical zone22 of a molded contact lens blank needed to give the target contact lens10 will preferably be 0.05 mm-0.50 mm, whereby it is possible toconsistently carry out the cutting process with a high degree ofaccuracy, and quickly and easily as well. When cutting contact lensblanks of single shape to form all of the contact lenses making up aseries of contact lenses, where the extent of cutting of the frontsurface optical zone 22 would be excessive, it would be possible toinstead employ two, three, or more forming molds 102 to make two, three,or more types of contact lens blanks. In this case, the upper mold 106could be standardized.

In FIGS. 4(a), (b), and (c) are shown a plurality of contact lenses 120a, 120 b, 120 c selected appropriately from among lenses making up aseries of contact lenses according to a second embodiment. As in thefirst embodiment, contact lenses 120 a, 120 b, 120 c have mutuallydifferent optical characteristics (e.g. refractive power) in the opticalzone, and by being combined appropriately make up a series of contactlenses. In FIG. 4, components identical in structure to those in thefirst embodiment are assigned the same symbols in the drawing, and arenot described in detail.

Specifically, contact lenses 120 (herein, in the case that specificsymbols a, b, c are absent, lenses a, b, and c are referred tocollectively) simply differ in terms of the diametrical locations of theback surface junction 32 and the second front surface junction 36, buthave optical zone 28 and second peripheral zone 44 shapes that aregenerally the same as in the first embodiment. In the first peripheralzone 42, for which the setting differs from that in the firstembodiment, the lens back surface 14 (portion composed of the innerperipheral portion of the back surface peripheral zone 18 and, in someinstances, an area equal to this plus the outer peripheral portion ofthe back surface optical zone 16) is established generally the same asin the first embodiment, with only the diametrical locations of the backsurface junction 32 and the second front surface junction 36 beingdifferent. In short, the characteristic element of contact lenses 120 ofthis embodiment differing from contact lenses 10 of the first embodimentis the surface shape of the first front surface peripheral zone 38 ofthe lens front surface 20.

In a contact lens 120 of this embodiment, the first front surfaceperipheral zone 38 has, by way of the illustrated cross sectional shapein the diametrical direction, a continuous, smoothly bowed surfacehaving no inflection point. The inner peripheral edge portion of thefirst front surface peripheral zone 38 connects so as to be continuousvia a common tangent with the outer peripheral edge portion of the frontsurface optical zone 22, at the first front surface junction 34 (theconnection point (X₁, Y₁) in FIG. 5). The outer peripheral edge portionof the first front surface peripheral zone 38 connects so as to becontinuous via a common tangent with the inner peripheral edge portionof the second front surface peripheral zone 40, at the second frontsurface junction 36 (the connection point (X₂, Y₂) in FIG. 5).

As shown in FIG. 5 depicting a specific shape for the peripheral zone 30designed according to this embodiment, like in FIG. 2 in the firstembodiment, over generally all of the lens front surface 20 from thefront surface optical zone 22 formed with a radius of curvature: Rfappropriate for producing the target optical characteristics in theoptical zone 28 to the second front surface peripheral zone 40 formedwith a radius of curvature: Rfp appropriate for achieving consistentwear qualities of all contact lenses 120 making up the series, a smoothbowed surface shape with no inflection point is effectively imparted bymeans of specific lens surface shape in the first front surfaceperipheral zone 38 connecting the front surface optical zone 22 with thesecond front surface peripheral zone 40.

In short, the shape of the front surface optical zone 22 is important interms of achieving target optical characteristics, and the shape of thesecond front surface peripheral zone 40 is important in terms ofadvantageously and consistently achieving target wear comfort and otherhandling properties. This embodiments specifically adjusts the shape ofthe first front surface peripheral zone 38, which has substantially noeffect or relatively small effect on optical characteristics and wearcomfort, while allowing freedom in terms of design of preferred shapefor the shapes of the front surface optical zone 22 and the second frontsurface peripheral zone 40. Thus, it is possible in all of the contactlenses 120 making up the series to maintain adequately good wear comfortwithout adversely affecting optical characteristics, while avoiding thepresence of inflection points on the lens surface, so as to achieve ahigher level of wear comfort.

The specific shape of the first front surface peripheral zone 38 may bederived employing any of various appropriate functions as thediametrical shape, for example; in particular, a non-spherical surfaceequation, multidimensional equation, triangular equation or the likecould be employed. Typically, the first front surface peripheral zone 38is located with its center of curvature on the lens center axis 12 atany point.

Specifically, it would be possible to employ for the first front surfaceperipheral zone 38 an annular bowed surface of diametrical shaperepresented, for example, by a cubic equation and targeted for rotationin relation to the lens center axis 12, whereby it is possible torelatively easily design a smooth bowed surface overall, such that theconnecting area with the second front surface peripheral zone 40 andfront surface optical zone 22 at the inner and outer peripheral edgeportions in the first front surface peripheral zone 38 have a commontangent.

Manufacture of contact lenses 120 of construction according to thisembodiment may of course advantageously employ method similar to thosein the first embodiment described previously.

Following is a description of a specific example of a design wherein, ina contact lens 10 described in the above embodiment, only the shape ofthe first front surface peripheral zone 38 differs, with the shape ofthe first front surface peripheral zone 38 in the diametrical directionbeing represented by a cubic equation, so as to connect with the frontsurface optical zone 22 and second front surface peripheral zone 38 atconnecting point having a common tangent.

In the following description employs X-Y orthogonal coordinates as shownin FIG. 5, wherein the lens center axis 12 is designated as the Y axis,and the diametrical line at a right angle to the center axis 12 isdesignated as the X axis.

First, the basic shape of the contact lens is established in thefollowing manner.

(i) Shape of Front Surface Optical Zone 22

The front surface optical zone 22 is a spherical surface represented byEq. {circle over (1)} below.X ²+(Y−K)² =FC ²  Eq. {circle over (1)}

-   -   FC: radius of curvature of front curve (spherical surface)    -   K: Y segment of front curve

Values of FC and K are calculated in advance by means of opticalcalculations (ray tracing or the like).

(ii) Coordinates of Outer Peripheral Portion Side (End Point Side) EndPortion of Front Surface Optical Zone 22

Coordinates of the outer peripheral edge portion (end point) of frontsurface optical zone 22 are designated (X₁, Y₁).

Values of X₁, Y₁ are calculated in advance, with consideration given tothe outside diameter dimension of the front surface optical zone 22.

(iii) Shape of Second Front Surface Peripheral Zone 40

The second front surface peripheral zone 40 is given an ellipticalsurface represented by Eq. {circle over (2)} below.X ² /M ²+(Y−L)² /N ²=1  Eq. {circle over (2)}

-   -   L: Y segment of center of ellipse    -   M: ellipse axis (X axis direction)    -   N: ellipse axis (Y axis direction)

Values of L, M, and N are calculated in advance on the basis of theestablished value for thickness of the peripheral zone 30.

(iv) Coordinates of Inner Peripheral Side (Start Point Side) End Portionof Second Front Surface Peripheral Zone 40

Coordinates of the inner peripheral edge portion (start point) of secondfront surface peripheral zone 40 are designated (X₂, Y₂).

Appropriate values of X₂, Y₂ are calculated in advance, within a rangesuch that the value of [radial dimension at location of second frontsurface junction 36: X₂/outer peripheral radial dimension of contactlens 120: DIA/2] is within the range 0.5-0.9.

(v) Cubic Equation Representing Calculated Diametrical Shape of FirstFront Surface Peripheral Zone 38

The cubic equation representing the shape of the first front surfaceperipheral zone 38 to be calculated contacts the front surface opticalzone 22 outer peripheral edge portion (end point) and the second frontsurface peripheral zone 40 inner peripheral edge portion (start point)at both edge portions (start point and end point) via a common tangent,and is represented by Eq. {circle over (3)} below.Y=AX ³ +BX ² +CX+D  Eq. {circle over (3)}

A, B, C and D in Eq. {circle over (3)} are variables to be calculated.

Here, calculation of A, B, C and D in Eq. {circle over (3)} in order toarrive at a shape for the first front surface peripheral zone 38 may beaccomplished in the following manner, for example.

First, the aforementioned Eq. {circle over (1)}, Eq. {circle over (2)}and Eq. {circle over (3)} are differentiated to arrive at the followingequations Eq. {circle over (4)}, Eq. {circle over (5)}, Eq. {circle over(6)}.dY/dX=−X/(Y−K)  Eq. {circle over (4)}dY/dX=−N ² X/(M ²(Y−L))  Eq. {circle over (5)}dY/dX=3AX ²+2BX+C  Eq. {circle over (6)}

Next, due to the condition that since there is a common tangent at point(X₁, Y₁), the value (dY/dX) of the slope of front surface optical zone22 represented by Eq. {circle over (4)} and the value (dY/dX) of theslope of the first front surface peripheral zone 38 represented by Eq.{circle over (6)} are equal, it is possible to derive Eq. {circle over(7)} below.−X ₁/(Y ₁ −K)=3AX ₁ ²+2BX ₁ +C  Eq. {circle over (7)}

(With the proviso that Y₁−K≈0)

Further, due to the condition that since there is a common tangent atpoint (X₂, Y₂), the value (dY/dX) of the slope of second front surfaceperipheral zone 40 represented by Eq. {circle over (5)} and the value(dY/dX) of the slope of the first front surface peripheral zone 38represented by Eq. {circle over (6)} are equal, it is possible to deriveEq. {circle over (8)} below.−N ² X ₂/(M ²(Y ₂ −L))=3AX ₂ ²+2BX ₂ +C  Eq. {circle over (8)}

-   -   (With the proviso that Y2−L≈0)

Since the first front surface peripheral zone 38 represented by Eq.{circle over (3)} passes through point (X₁, Y₁), it is possible toderive Eq. {circle over (9)} below.Y ₁ =AX ₁ ³ +BX ₁ ² +CX ₁ +D  Eq. {circle over (9)}

Also, since the first front surface peripheral zone 38 represented byEq. {circle over (3)} passes through point (X₂, Y₂), it is possible toderive Eq. {circle over (10)} below.Y ₂ =AX ₂ ³ +BX ₂ ² +CX ₂ +D  Eq. {circle over (10)}

Accordingly, the four-dimensional linear simultaneous equations given in{circle over (11)}-{circle over (14)} below can be determined from theabove four equations {circle over (7)}, {circle over (8)}, {circle over(9)} and {circle over (10)}.3X ₁ ² ×A+2X ₁ ×B+1×C+0×D=−X ₁/(Y ₁ −K)  Eq. {circle over (11)}3X ₂ ² ×A+2X ₂ ×B+1×C+0×D=−N ² X ₂/(M ²(Y ₂ −L)  Eq. {circle over (12)}X ₁ ³ ×A+X ₁ ² ×B+X ₁ ×C+1×D=Y ₁  Eq. {circle over (13)}X ₂ ³ ×A+X ₂ ² ×B+X ₂ ×C+1×D=Y ₂  Eq. {circle over (14)}

Thus, by solving the resultant simultaneous equations, it is possible tocalculate the variables: A, B, C, D in Eq. {circle over (3)} above, andthus to identify a shape for the first front surface peripheral zone 38.Solving of the simultaneous equations may be carried out easily usingCramer's rule or the like.

While the invention have been described in detail hereinabove in termsof certain preferred embodiments, the embodiments herein are merelyexemplary, and the invention should not be construed as being limited inany way to the specific disclosure of the embodiments herein. While notgiven individually herein, the present invention may be reduced topractice in various other modes incorporating variations, modificationsand improvements which would be apparent to those skilled in the art,and these embodiments will of course fall within the scope of theinvention insofar as they do not depart from the spirit thereof.

For example, the invention is applicable to both hard contact lenses andsoft contact lenses consisting of various kinds of materials. It is ofcourse possible to have an optical zone with toric power or the like.

In the peripheral zone, shape in the circumferential direction about thecenter axis could be varied so that when worn, the contact lens ispositioned in the circumferential direction. Even where such aperipheral zone shape which is not rotational symmetric about the centeraxis is employed, when making a series of contact lenses according tothe invention, the shape of the peripheral zone will be identical in allof the contact lenses making up the contact lens series.

Additionally, the invention relating to series contact lenses isadvantageously implemented in series contact lenses composed of aplurality of contact lens combinations for which mutually differentdiopter powers are established in a predetermined diopter power area,whereby there can be achieved the significant technical advantage thatexcellent wear comfort can be provided consistently in contact lensesover a diopter power distribution area of, for example, from 5 dioptersup to 10 diopters or more. However, there are various kinds of seriescontact lenses, and a series of contact lenses could also be composed onthe basis of the same lens material, for example. When implementing theinvention in such a series of contact lenses, it would not be necessaryto form all of the contact lenses of the series in accordance with theinvention, it being possible for the series to include specialty contactlenses imparted with special shape for a particular specialized purpose,for example. Specifically, when implementing the invention in a seriesof contact lenses composed, for example, on the basis of a given lensmaterial, and including in a given series one or several contact lenseshaving prism ballast functionality or contact lenses with exceedinglydifferent diopter powers for use under special conditions, the inventioncould be implemented in all of the lenses except for these specialtylenses.

Each contact lens making up a series of contact lenses in the inventionmay have aspheric shape for the optical zone front surface and backsurface, and/or the peripheral zone front surface and back surface. Indetail, the invention is also applicable, for example, to toric contactlenses or contact lenses of multifocal type or progressive type whosefront surface optical zone has aspheric shape.

As will be apparent from the preceding description, series contactlenses made in accordance with the present invention are based on thenovel technical concept, not contemplated in the past, of a standardizedshape for the peripheral zone, and due to the fact that the shape ofmost of the peripheral zone is identical for any contact lens of theseries, is able to provide the wearer with consistently good wearcomfort, tear fluid exchange, lens position stability, and the like,regardless of the optical characteristics of the optical zone selectedfor a particular wearer.

In contact lenses of structure according to the invention, by disposinga first peripheral zone of given thickness dimension extending in thediametrical direction between the optical zone and the second peripheralzone, it is possible to establish a small maximum thickness dimensionregardless of the diopter power of the optical zone, and to therebyreduce pressure on the conjunctiva and the eyelid, as well as lesseningthe tendency to catch during blinking, so that further improved wearcomfort may be achieved.

Additionally, according to the production method of the invention, whenmaking contact lenses with different optical characteristics, it ispossible to use a standard mold, thereby affording reductions inproduction costs, as well as imparting a fixed shape to the peripheralzone during molding of contact lenses with different opticalcharacteristics, so that the amount of deformation accompanyingpolymerization shrinkage, thermal shrinkage and the like during themolding process can be made uniform, thereby achieving excellent moldingaccuracy.

Industrial Applicability

As will be apparent from the description hereinabove, according to thepresent invention, there is now advantageously provided series contactlenses having an assortment of mutually different corrective diopterpowers or the like, each of which has in common good wear comfort andthe like, for high performance.

1. A series of contact lenses provided as an assorted plurality of contact lenses, each being formed with an optical zone in a lens center area and a peripheral zone in a lens peripheral area, by forming a back surface optical zone in a center portion of a lens back surface as well as forming a back surface peripheral zone to an outer peripheral side of a back surface optical zone, while forming in a center portion of a lens front surface a front surface optical zone as well as forming a front surface peripheral zone to an outer peripheral side of the front surface optical zone, and having a given diameter dimension but mutually different optical characteristics in the optical zone, the series of contact lenses being characterized in that in the assorted plurality of contact lenses, a shape of the lens back surface is identical for each lens, and a shape of an area extending a predetermined width in a diametrical direction of a peripheral portion in the front surface peripheral zone is identical for each lens, whereby while a shape of a portion extending a predetermined width in the diametrical direction of at least a peripheral portion in the peripheral zone is identical for each lens, a shape of the front surface optical zone differs among the lenses so that the optical characteristics of the optical zone differs among the lenses.
 2. A series of contact lenses according to claim 1, wherein different degrees of refractive power of the optical zone are established in the assorted plurality of contact lenses so that optical characteristics of the optical zone differ, and a diameter of the front surface optical zone is varied depending on differences in refractive power of the optical zones.
 3. A series of contact lenses according to claim 1, wherein the diameter of the front surface optical zone is set to within a range φ5 mm-φ12 mm in each of the assorted plurality of contact lenses.
 4. A series of contact lenses according to any claim 1, wherein different degrees of refractive power of the optical zone are established in the assorted plurality of contact lenses so that optical characteristics of the optical zone differ, and a center portion thickness of the front surface optical zone is varied depending on differences in refractive power of the optical zones.
 5. A series of contact lenses according to claim 4, wherein the center portion thickness of the optical zone is set to within a range of 0.02 mm-0.70 mm in each of the assorted plurality of contact lenses.
 6. A series of contact lenses according to claim 1, wherein different degrees of refractive power of the optical zone are established in the assorted plurality of contact lenses so that optical characteristics of the optical zone differ among these lenses, and the different degrees of refractive power of the optical zone are established within a range of −25 diopters to +25 diopters, with a difference of at least 5 diopters.
 7. A series of contact lenses according to claim 1, wherein in each of the assorted plurality of contact lenses, the front surface peripheral zone is composed of a first front surface peripheral zone situated on an inner peripheral side and a second front surface peripheral zone situated on an outer peripheral side, with a first peripheral zone being formed between the first front surface peripheral zone and the lens back surface, and with a second peripheral zone being formed between the second front surface peripheral zone and the lens back surface, the second peripheral zone having a shape that decreases in thickness gradually going towards the outer peripheral side, and wherein among the assorted plurality of contact lenses, each the second peripheral zone is of identical shape, and the first front surface peripheral zone forming the first peripheral zone has a smooth surface connecting to both the front surface optical zone and the second front surface peripheral zone in the diametrical direction at a continuous face having a common tangent.
 8. A series of contact lenses according to claim 7, wherein the first front surface peripheral zone is represented by a cubic curve in the diametrical direction.
 9. A series of contact lenses according to claim 1, wherein in each of the assorted plurality of contact lenses, the diameter of the front surface optical zone is smaller than the diameter of the back surface optical zone, while the front surface peripheral zone is composed of a first front surface peripheral zone situated on an inner peripheral side and a second front surface peripheral zone situated on an outer peripheral side, and has a shape with the first front surface peripheral zone being in a location generally corresponding to the back surface optical zone, and with the back surface optical zone offset.
 10. A series of contact lenses according to claim 9, wherein in each of the assorted plurality of contact lenses, a first peripheral zone of generally constant thickness is formed by the first front surface peripheral zone and the back surface optical zone, and the second front surface peripheral zone is situated in a location generally corresponding to the back surface peripheral zone, the second front surface peripheral zone and back surface peripheral zone forming a second peripheral zone that decreases in thickness going towards the outer peripheral side, the peripheral zone being composed of the first peripheral zone and the second peripheral zone, and wherein in among the assorted plurality of contact lenses, each the second peripheral zone has identical shape and each the first peripheral zone has identical thickness, while the diametrical width dimension of the first peripheral zones varies.
 11. A series of contact lenses according to claim 1, wherein a molding material for the assorted plurality of contact lenses is a soft material containing silicone.
 12. A series of contact lenses according to claim 1, wherein in the assorted plurality of contact lenses, the Young's modulus: y of the molding material is 0.2 MPa≦y≦2.0 MPa; and the value of average thickness: Tm of said peripheral zone is 0.05 mm≦Tm≦0.30 mm.
 13. A series of contact lenses according to claim 1, wherein in the assorted plurality of contact lenses, the Young's modulus: y of the molding material is 300 MPa≦y≦1500 MPa; and the value of average thickness: Tm of said peripheral zone is 0.08 mm≦Tm≦0.50 mm.
 14. A series of contact lenses according to claim 1, wherein the back surface peripheral zone has a curving surface with a radius of curvature greater than that of the back surface optical zone in the diametrical direction.
 15. A contact lens being formed with an optical zone in a lens center area and a peripheral zone in a lens peripheral area, by forming a back surface optical zone in a center portion of a lens back surface as well as forming a back surface peripheral zone to an outer peripheral side of a back surface optical zone, while forming in a center portion of a lens front surface a front surface optical zone as well as forming a front surface peripheral zone to an outer peripheral side of the front surface optical zone, the contact lens characterized in that the diameter of the front surface optical zone is smaller than the diameter of the back surface optical zone on the one hand, and the front surface peripheral zone is composed of a first front surface peripheral zone situated on an inner peripheral side and a second front surface peripheral zone situated on an outer peripheral side, while by having a shape wherein the first front surface peripheral zone is offset to the back surface optical zone, with a first peripheral zone of generally constant thickness being formed by the first front surface peripheral zone and back surface peripheral zone, and by situating the second front surface peripheral zone at a location generally corresponding to the back surface peripheral zone, the second front surface peripheral zone and back surface peripheral zone form a second peripheral zone that decreases in thickness going towards the outer peripheral side, the peripheral zone being composed of the first peripheral zone and the second peripheral zone.
 16. A method of manufacturing a contact lens constituting a series of contact lenses provided as an assorted plurality of contact lenses, each being formed with an optical zone in a lens center area and a peripheral zone in a lens peripheral area, by forming a back surface optical zone in a center portion of a lens back surface as well as forming a back surface peripheral zone to an outer peripheral side of a back surface optical zone, while forming in a center portion of a lens front surface a front surface optical zone as well as forming a front surface peripheral zone to an outer peripheral side of the front surface optical zone, and having a given diameter dimension but mutually different optical characteristics in the optical zone, the series of contact lenses being characterized in that in the assorted plurality of contact lenses, a shape of the lens back surface is identical for each lens, and a shape of an area extending a predetermined width in a diametrical direction of a peripheral portion in the front surface peripheral zone is identical for each lens, whereby while a shape of a portion extending a predetermined width in the diametrical direction of at least a peripheral portion in the peripheral zone is identical for each lens, a shape of the front surface optical zone differs among the lenses so that the optical characteristics of the optical zone differs among the lenses, wherein an entirety of the lens back surface including the back surface optical zone and the back surface peripheral zone, and an area of predetermined diametrical width of at least the outer peripheral portion of the front surface peripheral zone are shaped by molding.
 17. A method of manufacturing a contact lens, wherein when manufacturing a contact lens being formed with an optical zone in a lens center area and a peripheral zone in a lens peripheral area, by forming a back surface optical zone in a center portion of a lens back surface as well as forming a back surface peripheral zone to an outer peripheral side of a back surface optical zone, while forming in a center portion of a lens front surface a front surface optical zone as well as forming a front surface peripheral zone to an outer peripheral side of the front surface optical zone, an entirety of the lens back surface including the back surface optical zone and the back surface peripheral zone, and an area extending over predetermined diametrical width of at least the outer peripheral portion of the front surface peripheral zone are shaped by molding, and the front surface optical zone of the lens front surface is then shaped by cutting.
 18. A method of manufacturing a contact lens according to claim 17, wherein a minimum lens thickness in said optical zone of said lens front surface prior to shaping by cutting is set to within the range 0.05 mm-1.0 mm. 